The invention relates to test devices, and more particularly, to test devices for detecting current leakage between deep trench capacitors in DRAM devices, as well as test methods thereof.
DRAM is an important semiconductor device in the information and electronics industry. Most DRAM carries one transistor and one capacitor in a single DRAM cell. The memory capacity of the DRAM can reach 256 megabytes. Increased integration makes memory cell and transistor size reduction of necessary to accommodate DRAM with higher memory capacity and processing speed. A 3-D capacitor structure, such as a deep trench capacitor, can reduce occupied area on the semiconductor substrate, and is typically applied to the fabrication of DRAM with capacity of 64 megabytes and above.
Conversely, a conversional plane transistor structure covers a plurality of areas of the semiconductor substrate and cannot satisfy the demands for high integration.
FIG. 1 is a layout of conventional deep trench capacitors in a memory device. Deep trench capacitors 10 are disposed under passing word lines. Transistors 14 are electrically coupled to the storage nodes 16 of the capacitors 10 through the diffusion regions 18. The diffusion regions 20 are connected to plugs 22 coupled to bit lines (not shown). The transistors 14 are driven by word lines 12, and the channels thereunder are conductive when appropriate voltages are applied thereto. Consequently, the current produced between the diffusion regions 18 and 20 may flow into or out of the capacitors (storage nodes) 10.
FIG. 2 is a layout of a conventional memory device. As shown, bit line contacts 22 are connected in series by bit lines BL1, BL2 or BL3, and the adjacent deep trench capacitors 10A and 10B, disposed in parallel, can be regarded as a trench capacitor pair 11. Current technology can only detect leakage current between different trench capacitor pairs. For example, current leakage between the capacitor 10B of the trench capacitor pair 11-1 and the capacitor 10A of the trench capacitor pair 11-5, between the capacitor 10A of the trench capacitor pair 11-1 and the capacitor 10B of the trench capacitor pair 11-3, or between the capacitor 10B of the trench capacitor pair 11-1 and the capacitor 10A of the trench capacitor pair 11-4, can be detected by an APDM structure.
Current technology, however, cannot detect current leakage between the capacitors 10B and 10B in each trench capacitor pair 11.